Christopher G. Fletcher

• Doctor of Philosophy
• Professor (Associate) at University of Waterloo

This paper reviews developments for the Community Land Model, version 4 (CLM4), examines the land surface climate simulation of the Community Climate System Model, version 4 (CCSM4) compared to CCSM3, and assesses new earth system features of CLM4 within CCSM4. CLM4 incorporates a broad set of improvements including additions of a carbon-nitrogen (...

Variability in the extent of fall season snow cover over the Eurasian sector has been linked in observations to a teleconnection with the winter Northern Annular Mode pattern. Current generation GCMs do not capture this snow-circulation connection as part of their internal dynamics. So we instead explore the dynamics of this snow-circulation connec...

Future climate warming is virtually certain to bring about an increase in the frequency of heat extremes. Highway design and pavement selection are based on a temperature regime that reflects the local climate zone. Increasing heat extremes could, therefore, shift some areas into a different performance grade (PG) for pavement, and more-heat-resist...

The northern annular mode (NAM) influences wintertime climate variability in the Northern Hemisphere, and understanding the processes controlling its sign and amplitude is of critical importance. Mounting evidence supports a robust teleconnection between the El Niño-Southern Oscillation (ENSO) and the NAM, while internal variability generated in th...

Over the past decade, substantial progress has been made in improving our understanding of surface albedo feedbacks, where changes in surface albedo from warming (cooling) can cause increases (decreases) in absorbed solar radiation, amplifying the initial warming (cooling). The goal of this review is to synthesize and assess recent research into th...

The potential for complex systems to exhibit tipping points in which an equilibrium state undergoes a sudden and often irreversible shift is well established, but prediction of these events using standard forecast modelling techniques is quite difficult. This has led to the development of an alternative suite of methods that seek to identify signat...

Snow has significant impacts on springtime flooding, water resource management practices and the regional water-energy budget. In situ observations are considered some of the highest quality measurements of snow depth available, and are useful constraints for numerical weather prediction models and reanalysis system estimates of snow water equivale...

Remotely-sensed precipitation retrievals are critical for advancing our understanding of global energy and hydrologic cycles in remote regions. Radar reflectivity profiles of the lower atmosphere are commonly linked to precipitation through empirical power laws, but these relationships are tightly coupled to particle microphysical assumptions that...

The timing and rate of northern high latitude spring snowmelt plays a critical role in surface albedo, hydrology, and soil carbon cycling. Ongoing changes in the abundance and distribution of trees and shrubs in tundra and boreal ecosystems can alter snowmelt via canopy impacts on surface energy partitioning. It is unclear whether vegetation-relate...

Ongoing socio-economic developments and climatic change have been pressurizing the groundwater resource availability in the Abaya–Chamo lakes basin, Ethiopian Rift valley. The primary goals of the present study are: (1) to simulate the groundwater gradient and flow direction, (2) to calculate the groundwater balances and flux of the sub-major river...

As an idealized proxy for solar geoengineering, the GeoMIP G1 experiment forces Earth System Models with prescribed reductions in solar radiation to balance increases in atmospheric CO2. One key source of uncertainty is the magnitude of solar constant reduction required to offset a CO2 quadrupling. Here, we employ single‐forcing simulations with Co...

In August 2018, the European Space Agency (ESA) launched the Aeolus satellite, whose Atmospheric LAser Doppler INstrument (ALADIN) is the first space-borne Doppler wind lidar to regularly measure vertical profiles of horizontal line-of-sight (HLOS) winds with global sampling. This mission is intended to assess improvement to numerical weather predi...

Projections of future climate change to support decision‐making require Earth system models (ESMs) running at high spatial resolution, but at present this is computationally prohibitive. A major challenge is the calibration (parameter tuning) during the development of ESMs, which requires running large numbers of simulations to identify optimal val...

Remotely-sensed precipitation retrievals are critical for advancing our understanding of global energy and hydrologic cycles in remote regions. Radar reflectivity profiles of the lower atmosphere are commonly linked to precipitation through empirical power laws, but these relationships are tightly coupled to particle microphysical assumptions that...

Remote sensing snowfall retrievals are powerful tools for advancing our understanding of global snow accumulation patterns. However, current satellite-based snowfall retrievals rely on assumptions about snowfall particle shape, size and distribution which contribute to uncertainty and biases in their estimates. Vertical radar reflectivity profiles...

The potential for complex systems to exhibit tipping points in which an equilibrium state undergoes a sudden and potentially irreversible shift is well established, but prediction of these events using standard forecast modeling techniques is quite difficult. This has led to the development of an alternative suite of methods that seek to identify s...

Reanalysis products provide spatially homogeneous coverage for a variety of climate variables in regions where observational data are limited. However, very little validation of reanalysis soil temperatures in the Arctic has been performed to date, because widespread in situ reference observations have historically been unavailable there. Here we v...

Snow is a critical contributor to the global water-energy budget with impacts on springtime flooding and water resource management practices. Laser altimetry [light detection and ranging (LiDAR)] is a remote-sensing technique that has demonstrated skill in monitoring snow depth, but the expense of purchasing and transporting traditional LiDAR equip...

Changes in the quantity of terrestrial Arctic snow have far‐reaching implications for the global water‐energy budget, ecosystem development, and cold region flooding. Snow water equivalent (SWE) is a useful metric for monitoring these changes, however only a sparse observing network is available in the Arctic. Space‐based remote sensing offers the...

The newest iteration of the Canadian Earth System Model (CanESM5.0.3) has an effective climate sensitivity (EffCS) of 5.65 K, which is a 54 % increase relative to the model's previous version (CanESM2 – 3.67 K), and the highest sensitivity of all current models participating in the sixth phase of the coupled model inter-comparison project (CMIP6)....

In August 2018, the European Space Agency launched the Aeolus satellite, whose Atmospheric LAser Doppler INstrument (ALADIN) is the first spaceborne Doppler wind lidar to regularly measure vertical profiles of horizontal line-of-sight (HLOS) winds with global sampling. This mission is intended to assess improvement to numerical weather prediction p...

Projections of future climate change to support decision-making require high spatial resolution, but this is computationally prohibitive with modern Earth system models (ESMs). A major challenge is the calibration (parameter tuning) process , which requires running large numbers of simulations to identify the optimal parameter values. Here we train...

Snow and ice control programs are critical for the efficiency and safety of transportation systems in all winter climates. Tools that help road authorities plan for, assess, and communicate the relationship between climate and winter road maintenance (WRM) activities are needed. There is increasing evidence that the development of such Climate Serv...

CloudSat is often the only measurement of snowfall rate available at high latitudes, making it a valuable tool for understanding snow climatology. The capability of CloudSat to provide information on seasonal and subseasonal time scales, however, has yet to be explored. In this study, we use subsampled reanalysis estimates to predict the uncertaint...

The newest iteration of the Canadian Earth System Model (CanESM5.0.3) has an Effective Climate Sensitivity (ECS) of 5.65 kelvin, which is a 54 % increase relative to the model's previous version (CanESM2 – 3.67 K), and the highest sensitivity of all current models participating in the sixth phase of the coupled model inter-comparison project (CMIP6...

Snowfall affects the terrestrial climate system at high latitudes through its impacts on local meteorology, freshwater resources and energy balance. Precise snowfall monitoring is essential for cold countries such as Canada, and particularly in temperature-sensitive regions such as the Arctic; however, its size and remote location means the precipi...

An emergent constraint (EC) is a popular model evaluation technique, which offers the potential to reduce intermodel variability in projections of climate change. Two examples have previously been laid out for future surface albedo feedbacks (SAF) stemming from loss of Northern Hemisphere (NH) snow cover (SAFsnow) and sea ice (SAFice). These proces...

Snow is a critical contributor to Ontario's water-energy budget, with impacts on water resource management and flood forecasting. Snow water equivalent (SWE) describes the amount of water stored in a snowpack and is important in deriving estimates of snowmelt. However, only a limited number of sparsely distributed snow survey sites (n=383) exist th...

The extent to which decadal-to-multidecadal climate trends forced by carbon dioxide (\(\text{CO}_2\)) and anthropogenic aerosol (AER) emissions depend on the phase and amplitude of internal modes of climate variability, such as Atlantic Multidecadal Variability (AMV), is an open question. This study uses a fully coupled CMIP5-era general circulatio...

Soil moisture is a critical indicator for climate change and agricultural drought, but its measurement is challenging due to large variability with land cover, soil type, time, space and depth. Satellite estimates of soil moisture are highly desirable and have become more widely available over the past decade. This study investigates and compares t...

Plain Language Summary Snow on Arctic sea ice impacts global climate in many ways. Because the Arctic is a remote region, we have few direct measurements of snow depth on Arctic sea ice. We can use snow models, which take input of snowfall rates from numerical model‐based products that incorporate observations, to estimate this snow depth. However,...

Abstract Snow is a critical contributor to our global water and energy budget, with profound impacts for water resource availability and flooding in cold regions. The vast size and remote nature of the Arctic present serious logistical and financial challenges to measuring snow over extended time periods. Satellite observations provided by the Clou...

Abstract. Abstract. Snow is a critical contributor to Ontario's water-energy budget with impacts on water resource management and flood forecasting. Snow water equivalent (SWE) describes the amount of water stored in a snowpack and is important in deriving estimates of snowmelt. However, only a limited number of sparsely distributed snow survey si...

Purpose of Review Highlight significant developments that have recently been made to enhance our understanding of how snow responds to climate forcing and the role that snow plays in the climate system. Recent Findings Widespread snow loss has occurred in recent decades, with the largest decreases in spring. These changes are primarily driven by t...

Single-layer vegetation schemes in modern land surface models have been found to overestimate diurnal cycles in longwave radiation beneath forest canopies. This study introduces an empirical correction, based on forest-stand-scale simulations, which reduces diurnal cycles of sub-canopy longwave radiation. The correction is subsequently implemented...

Study region: The volcano-tectonic lakes basin of Abaya-Chamo is part of the Main Ethiopian Rift system and exhibits large variations in geomorphology, physiography and climate between the rift floor and the plateau. Study focus: Despite the importance of streamflow for water resources management and planning in the basin, many of the rivers there...

Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as the...

Many Earth system models contain substantial biases in the magnitude and seasonal cycle of the albedo of snow-covered surfaces. Various structural and parametric deficiencies have been identified as potential causes of these albedo biases, related to vegetation distribution and abundance, snow albedo, and the representation of snow interception by...

Single-layer vegetation schemes have been found to overestimate diurnal cycles in longwave radiation beneath forest canopies. This study derives a correction from forest stand-scale simulations, which reduces diurnal cycles of sub-canopy longwave radiation. Correction factors are subsequently implemented in land-only simulations of the Community La...

Climate sensitivity in Earth system models (ESMs) is an emergent property that is affected by structural (missing or inaccurate model physics) and parametric (variations in model parameters) uncertainty. This work provides the first quantitative assessment of the role of compensation between uncertainties in aerosol forcing and atmospheric paramete...

Boreal forests cover about a fifth of seasonally snow-covered land over the Northern Hemisphere. Enhancement of longwave radiation beneath coniferous forests has been found to impact the surface energy balance and rates of snowmelt. Although the skill of model-simulated snowmelt has been shown to be lower for forests than for open areas, model inte...

Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as the...

Climate sensitivity in Earth System Models (ESMs) is an emergent property that is affected by structural (missing or inaccurate model physics) and parametric (variations in model parameters) uncertainty. This work provides the first quantitative assessment of the role of compensation between uncertainties in aerosol forcing and atmospheric paramete...

The Canadian Sea Ice and Snow Evolution (CanSISE) Network is a climate research network focused on developing and applying state-of-the-art observational data to advance dynamical prediction, projections, and understanding of seasonal snow cover and sea ice in Canada and the circumpolar Arctic. This study presents an assessment from the CanSISE Net...

This study assesses the ability of the Canadian Seasonal to Interannual Prediction System (CanSIPS) and the Canadian Earth-system Model 2 (CanESM2) to predict and simulate snow and sea ice from seasonal to multi-decadal timescales, with a focus on the Canadian sector. To account for observational uncertainty, model structural uncertainty, and inter...

The northern polar stratosphere plays an important role in modulating wintertime near-surface temperatures in midlatitudes. Forecasting northern polar stratospheric variability therefore has the potential to extend the skill of seasonal winter weather forecasts. This research explores the utility of state-of-the-art statistical learning models for...

The two components of the tropical overturning circulation, the meridional Hadley circulation (HC) and the zonal Walker circulation (WC), are key to the re-distribution of moisture, heat and mass in the atmosphere. The mid-Pliocene Warm Period (mPWP; ∼ 3.3–3 Ma) is considered a very rough analogue of near-term future climate change, yet changes to...

Projections of 21st century Northern Hemisphere (NH) spring snow cover extent (SCE) from two climate model ensembles are analyzed to characterize their uncertainty. The Fifth Coupled Model Intercomparison Project (CMIP5) multi-model ensemble exhibits variability due to both model differences and internal climate variability, whereas spread generate...

The two components of the tropical overturning circulation, the meridional Hadley circulation (HC) and the zonal Walker circulation (WC), are key to the re-distribution of moisture, heat and mass in the atmosphere. The mid-Pliocene Warm Period (mPWP; ∼3–3.3 MY BP) is considered a useful analogue of near-term future climate change, yet changes to th...

Effectively modeling the influence of terrestrial snow on climate in general circulation models is limited by imperfect knowledge and parameterization of arctic and subarctic climate processes and a lack of reliable observations for model evaluation and improvement. This study uses a number of satellite-derived data sets to evaluate how well the cu...

The northern annular mode (NAM) characterizes a significant fraction of wintertime climate variability in the Northern Hemisphere. Understanding the processes governing changes in the NAM on interannual and longer timescales is therefore of critical importance. Previous work reveals a consensus around the negative NAM response to El Niño events (EL...

This study presents a comprehensive evaluation of snow albedo feedback (SAF) in two generations of climate models (CMIP3 and CMIP5). A comparison of the models is performed against a multi-observation-based reference dataset (mOBS) derived from the seasonal cycle of albedo, snow cover and temperature. The observed total SAF shows low uncertainty an...

Variation in snow albedo feedback (SAF) among CMIP5 climate models has been shown to explain much of the variation in projected 21st Century warming over Northern Hemisphere land. Prior studies using observations and models have demonstrated both considerable spread in the albedo, and a negative bias in the simulated strength of SAF, over snow-cove...

[1] Interannual variability in tropical sea surface temperatures (SSTs) associated with the El Niño–Southern Oscillation is linked to teleconnections with the Northern Annular Mode (NAM). Previous work highlighted that the sign and amplitude of the NAM response to tropical SSTs are controlled by the total wave activity entering the subpolar stratos...

During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing syst...

Snow albedo feedback (SAF) is important for global climate change, with strong regional impacts over northern continental areas. SAF calculated from the seasonal cycle is a good predictor of SAF in climate change among a suite of coupled climate models. A previous linear decomposition of the simulated total SAF (NET) found 80% was related to the al...

The elevated risk of collision while driving during precipitation has been well documented by the road safety community, with heavy rainfall events of particular concern. As the climate warms in the coming century, altered precipitation patterns are likely. The current study builds on the extensive literature on weather-related driving risks and dr...

Snow albedo feedback (SAF) is expected to amplify future climate change via changes to the surface energy balance, in particular the climate and hydrology of high latitude regions. However, the current generation of climate models shows a large spread in their projections of how strong future SAF will be. In this study, we use recent satellite obse...

Recent observational and modeling studies have demonstrated a link between eastern tropical Pacific Ocean (TPO) warming associated with the El Niñ o–Southern Oscillation (ENSO) and the negative phase of the wintertime northern annular mode (NAM). The TPO–NAM link involves a Rossby wave teleconnection from the tropics to the extratropics, and an inc...

Snow albedo feedback (SAF) is expected to have both global and regional impacts on future climate as atmospheric greenhouse gas concentrations increase. The global impact arises through changes to the climate sensitivity caused by decreases in surface and planetary albedo related to melting snow and ice. Regional impacts are likely to arise, at lea...

The suite of general circulation models (GCMs) in the Coupled Model Intercomparison Project (CMIP3) have been found not to reproduce the observed relationship between October Eurasian snow cover anomalies and the wintertime Northern Annular Mode (NAM). This apparent deficiency of GCMs is reexamined here based on analysis of observational data and G...

The classical problem of predicting the atmospheric circulation response to extratropical surface forcing is revisited in the context of the observed connection between autumnal snow cover anomalies over Siberia and wintertime anomalies of the Northern Annular Mode (NAM). Previous work has shown that in general circulation model (GCM) simulations i...

In the northern extratropics, seasonal prediction depends mainly on finding teleconnections linking modes of daily atmospheric variability with persistent sea-surface temperature (SST) anomalies in the Tropics. These links can be maintained for weeks, months or even years by, for example, El Nino/Southern Oscillation (ENSO) episodes or secular warm...

Snow albedo feedback (SAF) is expected to have both global and regional impacts on future climate, through changes to the climate sensitivity and through amplification of local land surface warming. This has important implications for the climate and hydrology of high latitude regions. Yet, the current generation of climate models shows a large spr...

Climate change is expected to cause a reduction in the spatial extent of snow cover on land. Recent work suggests that this will exert a local influence on the atmosphere and the hydrology of snow-margin areas through the snow-albedo feedback (SAF) mechanism. A significant fraction of variability among IPCC AR4 general circulation model (GCM) predi...

Climate change is expected to cause reductions in the amount and spatial extent of snow cover on land. Recent work suggests that this will exert a local influence on the atmosphere and the hydrology of snow- margin areas through the snow-albedo feedback (SAF) mechanism. A significant fraction of variability among IPCC AR4 general circulation model...

The transient atmospheric circulation response to fall season Siberia region snow forcing in an atmospheric general circulation model is investigated. The forcing generates a stratosphere-troposphere interaction response whose coupling to the surface on multiple week timescales depends on the state of the stratosphere prior to the initiation of the...

A statistical forecast model, referred to as the snow-cast (sCast) model, has been developed using observed October mean snow cover and sea level pressure anomalies to predict upcoming winter land surface temperatures for the extratropical Northern Hemisphere. In operational forecasts since 1999, snow cover has been used for seven winters, and sea...

In this paper we will discuss how continental-scale snow cover variations might force the extratropical stratosphere-troposphere interaction events highlighted by Baldwin and Dunkerton and others. These events consist of an annular-mode signature that starts in the stratosphere and progresses downward into the troposphere, where it persists for sev...

Recent proposed seasonal hindcast skill estimates for the winter North Atlantic Oscillation (NAO) are derived from different lagged predictors, NAO indices, skill assessment periods, and skill validation methodologies. This creates confusion concerning what is the best-lagged predictor of the winter NAO. To rectify this situation, a standardized co...

Recent observational studies provide strong evidence for lagged relationships between snow cover and subsequent Northern Hemisphere (NH) large-scale winter circulation patterns. However, these analyses typically employ relatively short time series of monthly mean data. This reduces the ability to determine accurately whether the snow forces the atm...